1. Field of the Invention
This invention relates to a four-wheel steering system for a vehicle in which both the front and rear wheels are turned in response to operation of the steering wheel.
2. Description of the Prior Art
There has been known a four-wheel steering system for a vehicle which comprises a steering mechanism for turning the front wheels, and a rear wheel turning mechanism for turning the rear wheels, and in which the steering force from the steering mechanism is transmitted to the rear wheel turning mechanism by way of a rod member to turn the rear wheels in response to turning of the front wheels.
In such a four-wheel steering system, the steering mechanism includes a rack bar which extends in the transverse direction of the vehicle and moves tie rods to turn the front wheels, and is provided with a first rack in mesh with a first pinion connected to the steering wheel and a second rack in mesh with a second pinion provided on the front end of the rod member by way of which the steering force is transmitted to the rear wheel turning mechanism.
As an intermesh adjustment mechanism for adjusting the intermesh between the rack and the pinion of each of said rack-and-pinion mechanisms, there has been known one in which the first and second pinions are positioned at a predetermined angle to each other and the rack bar is urged toward the pinions by a pair of resilient pressing means at portions corresponding to the respective rack-and-pinion mechanism, each resilient pressing means comprising a spring and a bearing member, for example. See Japanese Unexamined Patent Publication No. 58(1983)-122256, for example.
However the conventional intermesh adjustment mechanism is disadvantageous in that when intermesh adjustment of one of the rack-and-pinion mechanisms is completed and intermesh adjustment of the other rack-and-pinion mechanism is to be subsequently accomplished, the rack bar is deflected by the pressure from the resilient pressing means and side load is imparted to the bearing member of the resilient pressing means corresponding to said one rack-and-pinion mechanism to press the bearing member against the inner surface of a gear box accommodating it, thereby deforming the bearing member and/or the gear box. Further, if the first and second pinions are disposed at an angle other than 90.degree. due to limitations relating to the layout, the deflection of the rack bar can adversely affect the intermesh between the rack and the pinion of said rack-and-pinion mechanism to require readjustment.